A persistent problem concerning BUR is the inefficient venting of vapors which accumulate and are trapped below the roofing plies of a BUR system. These vapors, which may originate from trapped moisture or changes in temperature or humidity, can cause blistering and buckling, which effects may lead to failure of the membrane. Accordingly, it is desirable to provide a system of venting which allows escape of these vapors from surfaces below the roofing ply sheets.
Spot or strip mopping, which leaves venting channels at the ends of the strips, has been used; however, the application of this mopping procedure requires special techniques and skills, while at best the process is very time consuming. Heretofore, heavy perforated sheeting, having a granule impregnated lower layer has been employed as a base sheet over the roof deck to minimize this problem. Although bonded to the roof by a bonding agent which flows through the perforations, the successive strips of the base sheeting, normally overlaped two inches, are not bonded to one another. The completed roofing membrane thus has no tensile strength imparted at right angles to the direction of ply laying adjacent the base sheet layer.
Accordingly, it is an object of the present invention to overcome the above difficulties in an economical and commercially feasible manner.